README: add lgtm.com badges

Author: rfjakob

Makefile

@@ -23,7 +23,9 @@ format: cshatag
 	clang-format -i *.c
 
 README.md: cshatag.1 Makefile
-	@echo "[![Build Status](https://travis-ci.org/rfjakob/cshatag.svg?branch=master)](https://travis-ci.org/rfjakob/cshatag)" > README.md
+	@echo '[![Build Status](https://travis-ci.org/rfjakob/cshatag.svg?branch=master)](https://travis-ci.org/rfjakob/cshatag)' > README.md
+	@echo '[![Total alerts](https://img.shields.io/lgtm/alerts/g/rfjakob/cshatag.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/rfjakob/cshatag/alerts/)' >> README.md
+	@echo '[![Language grade: C/C++](https://img.shields.io/lgtm/grade/cpp/g/rfjakob/cshatag.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/rfjakob/cshatag/context:cpp)' >> README.md
 	@echo >> README.md
 	@echo '```' >> README.md
 	MANWIDTH=80 man ./cshatag.1 >> README.md

README.md

@@ -1,4 +1,6 @@
 [![Build Status](https://travis-ci.org/rfjakob/cshatag.svg?branch=master)](https://travis-ci.org/rfjakob/cshatag)
+[![Total alerts](https://img.shields.io/lgtm/alerts/g/rfjakob/cshatag.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/rfjakob/cshatag/alerts/)
+[![Language grade: C/C++](https://img.shields.io/lgtm/grade/cpp/g/rfjakob/cshatag.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/rfjakob/cshatag/context:cpp)
 
 ```
 CSHATAG(1)                       User Manuals                       CSHATAG(1)